Dental Tribune Middle East & Africa Edition No.2, 2016

Dental Tribune Middle East & Africa Edition | 2/2016 24 restorative Figure13:Prototypes typesupperarch Figure21:Anteriorcrownsleft handview Figure 17: Upper right restoration on fully ad- justablearticulator Figure 25:Intercuspal position with no anterior contacts Figure14:Prototypeslowerarch Figure22:Upperarchocclusalview Figure18:Upperleftrestorationonfullyadjust- ablearticulator Figure26:Upperanteriors Figure15:Upperprepguide Figure 23: Upper right quadrant with palatal ramps Figure19:Anteriorcrownsfront view Figure27:Upperanteriorsfinalview Figure16:Lowerprepguide Figure 24: Upper left quadrant with palatal ramps Figure20:Anteriorcrownsright handview Figure28:Loweranteriorsfinalview a flattened fossae-marginal ridge contact with ‘freedom in centric’ an- terior guidance and group function inlaterotrusive(working)excursion. Deflectivecontacts Though 90% of natural dentitions have a deflective occlusal contact or an occlusal ‘prematurity’ between centric related occlusion (CRO) and centric occlusion (CO), it is usually in the form of a slide that has both a vertical and horizontal component occurring in all three planes. Accord- ing to Ash and Ramfjord, the hori- zontal ‘long centric’, from centric re- lated occlusion to centric occlusion, should be incorporated into a resto- ration by means of a post restorative occlusaladjustment. Dawson illustrates the ‘freedom in centric’ concept within the lingual concavity of the maxillary anterior teeth. He redefines long centric as ‘freedom to close the mandible ei- ther into centric relation or slightly anterior to it without varying the vertical dimension at the anterior teeth’. Additionally, long centric ac- commodated changes in head posi- tionandposturalclosure(Mohlposi- tion). GnathologyversusPMS Gnathologists believe that once the condyles are positioned in retruded axis position (centric relation), any movement out of this position should disocclude the posterior seg- ment, thus nullifying any horizontal cusp-fossaeareacontact. This belief, combined with the immediate anterior disocclusion, forms the basis of a mutually pro- tected occlusion and limits tooth wear.ThePMSocclusalscheme,how- ever, encourages multiple occlusal contacts during lateral movements (group function or wide centre) and during protrusive movements (long centric). This may have the effect of increasingtoothwear.Itis,therefore, logical that the PMS occlusal scheme recommends that occlusal wear is physiological, not pathological as suggested by gnathologists. The task of adjusting maximum intercuspa- tion contacts in two different posi- tions on an articulator may result in a lack of precision in both positions. However, the masticatory system has the ability to adapt to various in- fluences and though, in the author’s opinion, the concept of gnathol- ogy will produce stable long-term results, some patients may require more freedom in their occlusion and the PMS concepts are not to be dismissed in these patients. Indeed, some PMS concepts such as waxing- up the curve of Spee and Monson prior to occlusal rehabilitation are incorporated into every day occlusal practice. Casestudy PatientAwasreferredtomeforafull mouth reconstruction and aesthetic improvements to her smile (Figures 1-3). Initial impressions, facebow and jaw registration were taken for mounted study models (Figure 4). The study models showed the de- gree of over-eruption of her anterior segmentsanddisturbancestotheoc- clusalplane(Figures5-8). Initial diagnostic waxing (Fig- ures 9-12), prototypes (Figures 13 and 14) and prep guides (Figures 15 and 16) were completed using a lower curveofSpeeofa4”radius(anatomi- cal average as recommended by the PMStechniques). Initial prototypes were placed with large palatal ramps on the up- per anterior teeth to allow anterior tooth contacts and thus an imme- diate disclusion style of occlusal schemeasrecommendedinthegna- thologicalapproach. During the course of the initial preparation and prototypes and after a period of stabilisation, the patient was struggling to come to terms with the palatal ramps from aspeechandcomfortpointofview. The decision was made to changetheocclusalschemetoaPMS ‘freedom in centric’ style approach where initial guidance in both left and right lateral excursions came from posterior teeth until such time as the canines contacted and then took over as canine guidance. In pro- trusion, a similar long centric was es- tablished on posterior teeth so that in protrusive movements the initial guidance was from the posterior teeth until such time as the incisors touched and then took over the fur- thersmoothprotrusivemovements. Thiswasachievedbyusingafullyad- justable articulator to complete the restorations(Figures17and18). Conclusions The definitive anterior crowns were made of Procera all ceramic (Nobel Biocare) (Figures 19-21). The posteri- ors were constructed of traditional porcelain fused to metal with large flat areas on the palatal cusps for the establishmentofboth‘longandwide centric’ (Figures 22-24) as in the new intercuspal position there were no anterior contacts (Figure 25) due to loss of the palatal ramps. The final aesthetic result can be seen in Fig- ures26to29. Occlusion and the various oc- clusal concepts have caused – and continue to cause – debate. Whilst theauthorhasbeentrainedthrough- out his career in the concepts of gna- thology, there is the recognition that other occlusal concepts, such as PMS and bilateral balance, may have a part to play in treatment of some patients. During the rest of this series, the principles of gnathology will be used in the treatment of the partial or full mouthreconstruction. Acknowledgements For the writing of this article on ad- vanced restorative techniques, the author would like to thank the fol- lowingpeoplefortheirhelp: Dr Ibrahim Hussain, BDS, M.Med.Sci. Implantology–implantsurgeon Dr Andrew Watson, BDS, MSc, special- istinendodontics MrBradleyMoore–dentaltechnician, ADSLaboratory,Harrogate. Figure29:Fullfacefinalview ◊Page20 ProfessorPaul TiptonBDS,MSc, DGDPRCS(UK) DENTALSURGEON VisitingProfessor ofRestorative andCosmetic Dentistry,Cityof LondonDental School www.colds.co.uk SPECIALISTINPROSTHODONTICS www.drpaultipton.co.uk TClinic@Manchester,London www.tclinic.co.uk TIPTONTRAININGLtd www.tiptontraining.co.uk President of theBritishAcademyof RestorativeDentistry(BARD) www.bard.uk.com